ON A PSEUDO-REBREATHING TECHNIQUE TO ASSESS THE VENTILATORY SENSITIVITY TO CARBON-DIOXIDE IN MAN

1. The ventilatory sensitivity to carbon dioxide obtained from a step‐ramp CO2 challenge was compared to the CO2 sensitivity from the steady‐state method. 2. Experiments were performed in nine healthy male subjects against a background of hyperoxia and in two subjects against a background of normoxia. 3. In each subject experiments were performed in which the stepwise increase in end‐tidal PCO2 above its resting value (A) was varied (range 0‐2 kPa) and the subsequent rate of rise of end‐tidal PCO2 in time (R) kept constant at 0.6 or 0.8 kPa min‐1. 4. The results of the hyperoxic experiments show that the slope of the non‐steady‐state ventilatory response to CO2 (Sn) is greatly influenced by the magnitude of A. An increase of A of 1 kPa results in a 54% increase of the ratio non‐steady‐state ventilatory CO2 sensitivity to steady‐state ventilatory CO2 sensitivity (Ss). The magnitude of R plays a minor role in determining Sn. The normoxic experiments gave similar results. 5. In experiments performed during hyperoxia Sn approximates Ss when the magnitude of A is 0.5 kPa. 6. The results are discussed and related to a physiological model. Simulations with representative values for the model parameters are in fair agreement with experimental values. © 1990 The Physiological Society